1987 Electronic A/C diagnostic codes
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5th Gear
Joined: Jan 2004
Posts: 5
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From: excelsior mn
1987 Electronic A/C diagnostic codes
My 1987 convertible's electronic ac/heater has a "flashing mode annunciator" where the exterior temp is displayed. This indicates a problem somewhere in the system. I've got the GM Electrical Diagnosis Service Manual Supplement for this car. Going thru the 9 diagnostic modes, these are the numbers displayed :
mode1 139
mode2 117
mode3 77
mode4 00
mode5 83
mode6 73
mode7 75
mode8 00
mode9 80
In the manual, I can't find out what these numbers mean. I seem to have a low blower speed / low airflow and was hoping that these diagnostics would confirm this. I'm stuck so if anyone out there can help me, it would be greatly appreciated. Recently, the car was in to the Chevrolet dealer and they even didn't bother running the diagnostics on the system. Thanks!
mode1 139
mode2 117
mode3 77
mode4 00
mode5 83
mode6 73
mode7 75
mode8 00
mode9 80
In the manual, I can't find out what these numbers mean. I seem to have a low blower speed / low airflow and was hoping that these diagnostics would confirm this. I'm stuck so if anyone out there can help me, it would be greatly appreciated. Recently, the car was in to the Chevrolet dealer and they even didn't bother running the diagnostics on the system. Thanks!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Mode 8 is the diagnostic mode and "00" means there's nothing wrong so I'd re-enter Diagnostics and once to Mode 8, press the Cool Button. The diagnostic codes are: 01 - open in the feedback from the temp door motor; 02 - Outside Temp Sensor open; 04 - Outside Temp Sensor shorted; 08 - Inside Temp Sensor open; 16 - Inside Temp Sensor shorted. If you can't get a code, check ground. It runs to the driver's side kick panel and is on a separate lug from the other grounds that terminate there. If it's good and there's no stored codes, you may need a new panel.
The other modes offer little if any info. See Section 1C1 - Electronic A/C in your Helms for further explanation of what the Modes mean, but basically they're just binary numbers for the position of the temp door. The Diagnostic Mode is more fully explained in 8A-68, Electronic A/C: Temp Controls.
There's no diagnostic code for the Blower. It's powered by a Module on the Evaporator housing. Low voltage signals are sent from the Control Panel and amplified by the Module. Check the brown or tan wire at the Module harness for about 2.5 volts on Blower Speed "1" - that's the input from the Panel. Check it for about 6 volts on Speed "10". Check the output to the Blower - purple or black red or whatever is hot at the Blower Motor - for about 4 volts at "1"; 12 volts at "10". If it has the input but the output is low, it's needs a new Module, though if the output is 0 volts, make sure the Module is powered up. That's from a fusible link behind the battery so check the red wire in the Module harness for battery voltage. If the input is wrong, usually it's the Panel unless there's 0 volts and then you need to ohm out the tan wire from the Module back to the Panel to make sure it's not open. If the input and outputs are correct but the speed is low, either the motor is worn out or the squirrel cage is broken or it may be dropping volts at the motor connector (look for discolored wiring), or the duct work seals inside the dash are gone and your cooling air is blowing inside of the dash and not out of the vents. Remove the passenger side hush panel and if the air flow is good around the ECM, take off the dash cover and wrap the duct work with duct tape or stuff the connectors with form rubber or whatever you can find at Home Depot to make a decent seal.
The other modes offer little if any info. See Section 1C1 - Electronic A/C in your Helms for further explanation of what the Modes mean, but basically they're just binary numbers for the position of the temp door. The Diagnostic Mode is more fully explained in 8A-68, Electronic A/C: Temp Controls.
There's no diagnostic code for the Blower. It's powered by a Module on the Evaporator housing. Low voltage signals are sent from the Control Panel and amplified by the Module. Check the brown or tan wire at the Module harness for about 2.5 volts on Blower Speed "1" - that's the input from the Panel. Check it for about 6 volts on Speed "10". Check the output to the Blower - purple or black red or whatever is hot at the Blower Motor - for about 4 volts at "1"; 12 volts at "10". If it has the input but the output is low, it's needs a new Module, though if the output is 0 volts, make sure the Module is powered up. That's from a fusible link behind the battery so check the red wire in the Module harness for battery voltage. If the input is wrong, usually it's the Panel unless there's 0 volts and then you need to ohm out the tan wire from the Module back to the Panel to make sure it's not open. If the input and outputs are correct but the speed is low, either the motor is worn out or the squirrel cage is broken or it may be dropping volts at the motor connector (look for discolored wiring), or the duct work seals inside the dash are gone and your cooling air is blowing inside of the dash and not out of the vents. Remove the passenger side hush panel and if the air flow is good around the ECM, take off the dash cover and wrap the duct work with duct tape or stuff the connectors with form rubber or whatever you can find at Home Depot to make a decent seal.
